1. Field of the Invention:
This invention relates to liquid-metal fast breeder reactors of the double-pool type and, in particular, to an assembly of flow couplers or primary liquid metal pumps particularly adapted for such reactors
2. Reference to Co-pending Applications
Reference is made to the following co-pending, commonly assigned patent applications
(1) U.S. Ser. No. 822,183, entitled "Electromagnetic Flow Coupler for Regulating Flow Rate/Pressure, " filed Jan. 24, 1986 in the names of C. C. Alexion, A. R. Keeton and R. D. Nathenson; now U.S. Pat. No. 4,688,996;
(2) U.S. Ser. No. 875,150, entitled "A Pump/Intermediate Heat Exchanger Assembly For a Liquid Metal Reactor, " filed June 17, 1986 in the names of R. D. Nathenson, C. C. Alexion and W. C. Sumpman; now allowed;
(3) U.S. Ser. No. 875,151, entitled "Pump/Heat Exchanger Assembly for Pool-Type Reactor " filed June 17, 1986 in the names of R. D. Nathenson and R. M. Slepian; and
(4) U.S. Ser. No. 896,028, entitled "A Magnetofluidynamic Generator for a Flow Coupler " filed Aug. 13, 1986 in the name of R. M. Slepian, now U.S. Pat. No. 4,753,576.
3. Description of the Prior Art:
Early in the development of the liquid-metal fast breeder or nuclear reactor (LMFBR), it was recognized that liquid metals could be pumped by electromagnetic (EM) pumps. Such EM pumps offer the advantages of inherent simplicity and the lack of moving parts as compared with conventional, rotating impeller pumps. Such mechanical pumps have inherent problems associated with vibration or thermal distortion in areas of closely toleranced moving parts, such as bearings or seals. Furthermore, cavitation problems associated with a rotating impeller of mechanical pumps do not exist in an EM pump.
One such EM pump, known as a flow coupler, is particularly adapted to pump the primary flow of liquid metal to be heated by the core of a nuclear reactor. Such flow couplers transfer the internal energy of an intermediate flow of liquid metal to the primary flow, driving or pumping the primary flow in
Early examples of such flow couplers are described U.S. Pat. No. 2,715,190 of Brill and UK Pat. No. 745,460 of Pulley. In a typical flow coupler, a driven liquid metal in the intermediate flow is directed through a generator duct of the flow coupler. Adjacent to the generator duct is a pump duct, through which flows the primary flow. The intermediate and primary flows of liquid metal within the generator and pump ducts are exposed to a common magnetic field. Passage of the first flow through the common magnetic field generates a relatively low voltage, which produces a large current in the generator duct to be applied to the pump duct by a short, low resistance electrode disposed between the generator and pump ducts and by return conductors disposed on either side of the ducts. Interaction of the resulting high current in the pump duct with the common magnetic field drives the primary flow in the pump duct. In this manner, the intermediate flow of the liquid metal in the generator duct is "coupled " to the primary flow of the liquid metal in the pump duct. The use of such flow couplers in LMFBR systems is described in "Sodium Electrotechnology at the Risley Nuclear Power Development Laboratories", by D. F. Davidson et al., NUCLEAR ENERGY, 1981, Volume 20, February, no. 1, pp. 79-90. U.S. Pat. No. 4,469,471 of A. R. Keeton, et al. describes an improved embodiment of such a flow coupler.
In U.S. Pat. No. 4,412,785 of W. G. Roman, there is described a flow coupler/heat exchanger assembly for use with a nuclear reactor. The assembly forms an annular region between inner and outer shells. A plurality of tube sets is disposed within the annular region, with relatively large spaces between adjacent tube sets. A magnetic field is established in a radial direction through the annular region. A first conductive fluid, e.g. the intermediate liquid metal, is pumped through the spaces between the tube sets by an enlarged intermediate pump. A second conductive fluid, e.g. the primary liquid metal, is introduced into the tube sets. The radial magnetic flux couples the flow of intermediate liquid metal with the flow of primary liquid metal. The externally pumped flow of the intermediate liquid metal in the spaces between the tube sets through the radial magnetic flux, produces a voltage and a current in a circumferential direction about the annular region. The current passes through the adjacent tubes and the primary liquid metal therein, producing a driving force in the opposite direction, whereby the primary liquid metal is driven or pumped.
In a publication entitled, "High-Efficiency DC Electromagnetic Pumps and Flow Couplers For LMFBRs, " EPRI NP-1656, TPS 79-774, Final Report, January 1981, by I. R. McNab and C. C. Alexion, there is described an integral assembly of a heat exchanger and a flow coupler for a pool-type LMFBR. The flow coupler includes a plurality of duct modules disposed in a circle, with a magnetic field coil disposed between adjacent duct modules. Each duct module includes a pump duct through which the primary liquid metal flows and a generator duct through which the intermediate liquid metal flows in an opposite direction. The magnetic flux generated by the magnetic field coil is directed by an iron circuit to form a circular magnetic field through all of the duct modules. In one embodiment, the intermediate liquid metal is introduced into a centrally disposed inlet and directed downwardly to be introduced to an intermediate heat exchanger comprised of a plurality of vertically oriented tubes. The intermediate liquid metal is then directed upward and about these tubes, before being introduced into each of the generator ducts. The primary flow of liquid metal is directed downwardly through the pump ducts, exiting the pump ducts and being introduced into the tubes of the intermediate heat exchanger, flowing downwardly therethrough, before being discharged and recirculated to the nuclear core. It is contemplated that the flow coupler may be located beneath such an intermediate heat exchanger.
The above-identified application entitled, "A Pump/Intermediate Heat Exchanger Assembly For A Liquid Metal Reactor, " describes a plurality of flow coupler/heat exchanger assemblies disposed in a circular array within a nuclear reactor. In such an assembly, the flow coupler is disposed beneath the intermediate heat exchanger and in a co-linear relationship therewith. The primary liquid metal is directed from the reactor core and is introduced into the intermediate heat exchanger flowing down through an array of tubes enclosed in an annular cavity of the intermediate heat exchanger. The intermediate liquid metal is fed into the assembly via a centrally disposed "downcomer " pipe through the intermediate heat exchanger to the flow coupler and, in particular, to a first plenum for distributing the intermediate liquid metal to a plurality of flow couplers or duct modules, each comprised of one or more sets of pump and generator ducts. The intermediate liquid metal exits the first plenum being directed up in parallel through the generator ducts of the flow coupler modules. The intermediate liquid metal exiting the pump ducts is collected in a second plenum before being introduced into the annular cavity to be heated by the primary liquid metal flowing downwardly through the tubes. After being heated, the intermediate liquid metal is discharged and directed to a steam generator. The cooled, primary liquid metal is discharged from the tubes into a third plenum, before it is directed downwardly in parallel through the plurality of pump ducts, whereby the cooled, primary liquid metal is directed at relatively high pressure, i.e. pumped, into an annular plenum at the bottom of the nuclear reactor for return to the reactor core.
In the above referenced patent application entitled, "A Magnetofluidynamic Generator for a Flow Coupler", there is described a primary liquid metal pump comprised of a plurality of flow couplers disposed in a circular array, each flow coupler including at least one primary duct and one intermediate duct for receiving respectively flows of an intermediate liquid metal and a primary liquid metal. A field coil is disposed between each set of ducts and is energized by an auxiliary coil excitation generator, including a bootstrap liquid metal generator duct and means for generating an auxiliary magnetic field though the bootstrap generator duct. A portion of the flow of the intermediate liquid metal is directed through the bootstrap generator ducts to interact with the auxiliary magnetic field, whereby a flow of current is generated across the bootstrap generator duct and applied to excite the field coils.
In a double-pool type reactor, as will be explained in detail below, the primary liquid metal is placed in a primary vessel also containing the reactor core, the primary liquid metal pumps, and the intermediate heat exchangers. The intermediate liquid metal is placed in a secondary vessel, which surrounds the primary vessel and contains the secondary pumps and steam generators. In the prior art double-pool-type reactors, the mechanical-type primary liquid metal pumps and the intermediate heat exchangers are disposed in an annulus surrounding the reactor core. In order to substitute a flow coupler for the prior art mechanical primary liquid metal pumps, it is necessary to reconfigure the shape of such flow couplers, as well as to reconfigure the magnetic field and conduits for conveying the primary and intermediate liquid metals.